Endotracheal tubes are inserted in the trachea of patients and the outer end is connected to a source of respiratory gas. Such tubes are available in a number of sizes each to fit a different sized trachea. However, it is not possible to match supply tube and trachea size sufficiently, to prevent the outflow of respiratory gas around the outside of the tube. To prevent such flow, some supply tubes are fitted with an inflatable annular balloon which surrounds the respiratory gas flow tube and is commonly called a "cuff." In what has become the standard form of endotracheal tube, an auxilliary tube or passageway is included inside the respiratory gas supply tube. This auxilliary passage opens to the interior of the cuff and extends inside the respiratory gas flow tube to a point near the supply end. At that point, a separate tube is brought through the wall of the respiratory gas flow tube where it is connected to a syringe or other implement by which air may be forced into the cuff.
Such cuffs are entirely effective to prevent leakage past the end of the tracheal tube if inflated in sufficient degree. They present a problem, however, if the cuff is overinflated. The cuff will, in that case, press against the tracheal wall and damage its tissue. Often, the tube by which the cuff is inflated includes, or is connected to, an accumulator balloon. The appearance or the feel of the accumulator provides an indication of the pressure level in the cuff. Use of the accumulator is of some use in avoiding injury to the trachea but only at the expense of added complexity. A check valve is required in the filling line along with some means for violating the check valve or otherwise relieving the pressure in the cuff.
Cuffs fall into one of two classes. Some of them are made of a resilient material formed such that, in relaxed condition, the cuff remains ballooned to larger diameter than the flow tube. The other kind of cuff is formed of a substantially pliant material which exhibits little resilience, at least in the sense that it can be inflated without stretching the material from which the cuff is formed.
The fact that the inflatable cuff can cause injury has not gone unnoticed. A number of attempts have been made to find a self-inflating cuff whose inflation would be accomplished by "back pressure" exerted by respiratory gas and, therefore, would apply a pressure to the trachea that was related to supply pressure. These self-inflating cuffs operate like parachutes or, when made of resilient material that tends to balloon outwardly, with a combination of umbrella and parachute action. However, none of these self-inflating forms have found acceptance, apparently because of non-uniformity in their performance and because of failure to inflate until back pressure reaches a relatively high value.
Whether the end tracheal tube includes a cuff or not, it has been almost universal to form the respiratory gas supply tube from a length of tubing which is cut to length usually by cutting the inner distal end on the bias. Modern tubes often include a hole formed by punching through the side wall of the supply tube near the bias opening. The added opening is often called a "Murphy eye" and its purpose is to ensure that there can be a flow opening even if the bias opening becomes blocked. Any failure to eliminate sharp edges at the bias opening and Murphy eye presents a further opportunity for injury to the trachea tissue.
The invention provides an improved inner end for tracheal tubes and an improved cuff and cuff inflating arrangement.